Re: [PATCH] nfsd: check for oversized NFSv2/v3 arguments

[NeilBrown <neilb@suse.com>]

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On Tue, Apr 25 2017, J. Bruce Fields wrote:

>> > +	if (!*(rqstp->rq_next_page))
>> > +		return 0;
>> 
>> Why the extra parentheses?  "->" is at the highest precedence level for C.
>
> I've been doing this stuff enough years, you'd think I'd have bothered
> to memorize the C operator precedence table by now.
>
> Anyway, this change is actually unrelated and not entirely necessary;
> dropped.
>
>> i.e. either keep it simple (like the v2 code) or make it tidy (with head
>> and tail), but not half-and-half??
>
> What the heck, let's go all out.

Looks good, thanks.


>
> You only live once!

:-)

NeilBrown


>
> --b.
>
> commit db44bac41bbf
> Author: J. Bruce Fields <bfields@redhat.com>
> Date:   Tue Apr 25 16:21:34 2017 -0400
>
>     nfsd4: minor NFSv2/v3 write decoding cleanup
>     
>     Use a couple shortcuts that will simplify a following bugfix.
>     
>     Cc: stable@vger.kernel.org
>     Signed-off-by: J. Bruce Fields <bfields@redhat.com>
>
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index dba2ff8eaa68..d18cfddbe115 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -358,6 +358,8 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
>  {
>  	unsigned int len, v, hdr, dlen;
>  	u32 max_blocksize = svc_max_payload(rqstp);
> +	struct kvec *head = rqstp->rq_arg.head;
> +	struct kvec *tail = rqstp->rq_arg.tail;
>  
>  	p = decode_fh(p, &args->fh);
>  	if (!p)
> @@ -377,9 +379,8 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
>  	 * Check to make sure that we got the right number of
>  	 * bytes.
>  	 */
> -	hdr = (void*)p - rqstp->rq_arg.head[0].iov_base;
> -	dlen = rqstp->rq_arg.head[0].iov_len + rqstp->rq_arg.page_len
> -		+ rqstp->rq_arg.tail[0].iov_len - hdr;
> +	hdr = (void*)p - head->iov_base;
> +	dlen = head->iov_len + rqstp->rq_arg.page_len + tail->iov_len - hdr;
>  	/*
>  	 * Round the length of the data which was specified up to
>  	 * the next multiple of XDR units and then compare that
> @@ -396,7 +397,7 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
>  		len = args->len = max_blocksize;
>  	}
>  	rqstp->rq_vec[0].iov_base = (void*)p;
> -	rqstp->rq_vec[0].iov_len = rqstp->rq_arg.head[0].iov_len - hdr;
> +	rqstp->rq_vec[0].iov_len = head->iov_len - hdr;
>  	v = 0;
>  	while (len > rqstp->rq_vec[v].iov_len) {
>  		len -= rqstp->rq_vec[v].iov_len;
> diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c
> index 41b468a6a90f..59bd88a23a3d 100644
> --- a/fs/nfsd/nfsxdr.c
> +++ b/fs/nfsd/nfsxdr.c
> @@ -280,6 +280,7 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
>  					struct nfsd_writeargs *args)
>  {
>  	unsigned int len, hdr, dlen;
> +	struct kvec *head = rqstp->rq_arg.head;
>  	int v;
>  
>  	p = decode_fh(p, &args->fh);
> @@ -300,9 +301,8 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
>  	 * Check to make sure that we got the right number of
>  	 * bytes.
>  	 */
> -	hdr = (void*)p - rqstp->rq_arg.head[0].iov_base;
> -	dlen = rqstp->rq_arg.head[0].iov_len + rqstp->rq_arg.page_len
> -		- hdr;
> +	hdr = (void*)p - head->iov_base;
> +	dlen = head->iov_len + rqstp->rq_arg.page_len - hdr;
>  
>  	/*
>  	 * Round the length of the data which was specified up to
> @@ -316,7 +316,7 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
>  		return 0;
>  
>  	rqstp->rq_vec[0].iov_base = (void*)p;
> -	rqstp->rq_vec[0].iov_len = rqstp->rq_arg.head[0].iov_len - hdr;
> +	rqstp->rq_vec[0].iov_len = head->iov_len - hdr;
>  	v = 0;
>  	while (len > rqstp->rq_vec[v].iov_len) {
>  		len -= rqstp->rq_vec[v].iov_len;
> commit 13bf9fbff0e5
> Author: J. Bruce Fields <bfields@redhat.com>
> Date:   Fri Apr 21 15:26:30 2017 -0400
>
>     nfsd: stricter decoding of write-like NFSv2/v3 ops
>     
>     The NFSv2/v3 code does not systematically check whether we decode past
>     the end of the buffer.  This generally appears to be harmless, but there
>     are a few places where we do arithmetic on the pointers involved and
>     don't account for the possibility that a length could be negative.  Add
>     checks to catch these.
>     
>     Reported-by: Tuomas Haanpää <thaan@synopsys.com>
>     Reported-by: Ari Kauppi <ari@synopsys.com>
>     Reviewed-by: NeilBrown <neilb@suse.com>
>     Cc: stable@vger.kernel.org
>     Signed-off-by: J. Bruce Fields <bfields@redhat.com>
>
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index d18cfddbe115..452334694a5d 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -369,6 +369,8 @@ nfs3svc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
>  	args->count = ntohl(*p++);
>  	args->stable = ntohl(*p++);
>  	len = args->len = ntohl(*p++);
> +	if ((void *)p > head->iov_base + head->iov_len)
> +		return 0;
>  	/*
>  	 * The count must equal the amount of data passed.
>  	 */
> @@ -472,6 +474,8 @@ nfs3svc_decode_symlinkargs(struct svc_rqst *rqstp, __be32 *p,
>  	/* first copy and check from the first page */
>  	old = (char*)p;
>  	vec = &rqstp->rq_arg.head[0];
> +	if ((void *)old > vec->iov_base + vec->iov_len)
> +		return 0;
>  	avail = vec->iov_len - (old - (char*)vec->iov_base);
>  	while (len && avail && *old) {
>  		*new++ = *old++;
> diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c
> index 59bd88a23a3d..de07ff625777 100644
> --- a/fs/nfsd/nfsxdr.c
> +++ b/fs/nfsd/nfsxdr.c
> @@ -302,6 +302,8 @@ nfssvc_decode_writeargs(struct svc_rqst *rqstp, __be32 *p,
>  	 * bytes.
>  	 */
>  	hdr = (void*)p - head->iov_base;
> +	if (hdr > head->iov_len)
> +		return 0;
>  	dlen = head->iov_len + rqstp->rq_arg.page_len - hdr;
>  
>  	/*
>
> --
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